//对象转查询字符串
function objToSearchString(obj) {
    var str = ''
    for (var key in obj) {
        str += `${key}=${obj[key]}&`;
    }
    return str.slice(0, str.length - 1);
}

//封装ajax函数
function ajax(method, url, params) {
    return new Promise((resolve, reject) => {
        //1.创建请求对象
        var xhr = new XMLHttpRequest()
        //2.配置请求对象
        xhr.open(method, method == 'get' ? url + "?" + objToSearchString(params) : url);
        //3.设置回调函数
        xhr.onreadystatechange = function () {
            if (xhr.readyState == 4) {
                resolve(JSON.parse(xhr.responseText));
            }
        }
        //4.发送请求
        //设置请求头
        xhr.setRequestHeader('content-type', 'application/x-www-form-urlencoded');
        xhr.send(method == 'get' ? null : objToSearchString(params));
    })
}
